4. The 1990 emissions from energy production and use are estimated
by Marland et al. (1999) at 5.9 GtC excluding cement production. It appears
as if four scenarios also include deforestation, which might explain relatively
large differences in the base-year emissions compared to the other scenarios.
Excluding these four scenarios, the 1990 base-year values in the scenarios reviewed
range from 4.8 to 6.4 GtC. With the four scenarios the range is from 4.8 to
7.4 GtC.

5. Some of the scenarios may also include CO2 emissions from
industrial sources. Since non-energy-related industrial emissions are very low
compared to the energy-related CO2 emissions, their impact on the results of
the statistical analyses is negligible. It also appears as if four scenarios
also include deforestation. These scenarios tend to cluster around the median
and none occur in the tails of the scenario frequency distribution. Therefore,
they have very little influence on the range.

6. The issue of large differences in the base year quantifications
across the range of scenarios is discussed in Chapter 4,
in which are presented the new SRES scenarios as developed by six different
modeling approaches utilizing different base-year specifications.

7. Not all 256 scenarios that report global CO2 emissions cover
the whole period to the year 2100.

9. Values are shown also as indexed to 1990 values, since model
base years and base-year values differ.

10. Note that the highest scenario in the database reports
3400 EJ for primary energy consumption by 2100. Relative to the base year of
this scenario (340 EJ), this level corresponds to a 10-fold increase. However,
relative to the base-year value including non-commercial biomass (370 EJ), this
level corresponds to a nine-fold increase only.